The present invention relates to a flux cored wire for welding a ferrite stainless steel, in which the cracking resistant property and the corrosion resistant property are superior.
The components of the automobile gas exhaust system such as muffler and the like are generally made of a ferrite stainless steel. However, when this ferrite stainless steel is welded, the toughness of the welded portion is degraded, and therefore, cracks are liable to be formed. Accordingly, for welding the ferrite stainless steel, efforts have been concentrated on developing a welding wire which is superior to the cracking resistance and to the corrosion resistance.
For this purpose, conventionally solid wires have been used in welding the ferrite stainless steel. However, coming recently, the flux cored wire came to be widely used, because the flux cored wire gives a superior welding workability compared with the solid wire. However, even if the flux cored wire is used to weld the ferrite stainless steel, much slag is generated on the welded portion.
Japanese Patent Hei-5-30557 discloses a technique in which the generation of the slag is decreased during the welding of the ferrite stainless steel. In this technique, a flux cored wire is presented, in which the solution of the problem of the slag generation is aimed by limiting the contents of the slag forming agent, and in which the aggravation of the welding workability is aimed to be overcome by properly controlling the metal ingredients.
Another example of the disclosure of the flux cored wire for welding the ferrite stainless steel is Japanese Patent Application Laid-open No. Hei-9-85491. In this technique, the flux cored wire includes in weight %: 0.07xcx9c2.0% of Si, 14.5xcx9c17.0% of Cr, 0.01xcx9c1.0% of Al, 0.05xcx9c2.0% of Ti, 0.02xcx9c0.1% of N, 0.005xcx9c0.5% of F, and a balance of Fe and other unavoidable impurities. The unavoidable impurities includes: 0.10% or less of C, 0.2% or less of Nb, and 6.0% or less of Mn. This flux cored wire is improved in the oxidation resistant property and in the welding cost curtail.
The above described flux cored wires for welding the ferrite stainless steel are effective in improving the corrosion resistant property and the cracking resistant property to a certain degree. However, it is definitely limitative in attaining to a high corrosion resistant property and a high cracking resistant property.
The present invention is intended to overcome the above described disadvantages of the conventional techniques.
Therefore it is an object of the present invention to provide a flux cored wire for welding the ferrite stainless steel, in which the corrosion resistant property and the cracking resistant property are superior.
The present inventor carried out much researches and experiments to solve the problem of the cracking resistant property of the deposited metal, which is encountered after welding the ferrite stainless steel. As a result, the present inventor found the following fact. That is, it is important to limit the contents of oxygen and nitrogen among the ingredients of the welding wire, and to decide the total content of them in relation to the content of chrome. Therefore, the present inventor came to propose the present invention. That is, in the flux cored wire for welding the ferrite stainless steel, the contents of oxygen and nitrogen are controlled to the optimum levels, and the value which is defined by [(O+N)xc3x97Cr] is controlled to be 0.8 or less.
Therefore, in achieving the above object, the flux cored wire for welding a ferrite stainless steel according to the present invention includes in weight %: 0.04% or less of C, 0.1xcx9c1.0% of Si, 0.1xcx9c1.0% of Mn, 0.02% or less of P, 0.02% or less of S, 10xcx9c25% of Cr, 0.3xcx9c1.5% of Ti+Nb, 0.04% or less of N, 0.04% or less of O, and a balance of Fe and other unavoidable impurities, wherein a value defined by [(O+N)xc3x97Cr] is 0.8 or less.